Power transmission chain pin and manufacture method thereof

ABSTRACT

A manufacture method of a power transmission chain pin includes a work step of working a bar-like member of a predetermined length into a pin having a final sectional shape and a final end portion shape with a guide portion to facilitate a press-fitting operation by a cold forging work. At this time, the manufacture method does not include a grinding step of grinding an end portion of the bar-like member of the predetermined length by a grinding stone.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power transmission chain pin and amanufacture method thereof, and more specifically, to a powertransmission chain pin suitable for a continuously variable transmission(CVT) of a vehicle such as an automobile and a manufacture methodthereof.

2. Related Art

As shown in FIG. 9, as a continuously variable transmission for anautomobile, there is a known chain type continuously variabletransmission including a drive pulley (2) which has a stationary sheave(2 a) and a movable sheave (2 b) and which is disposed in an engine; adriven pulley (3) which has a stationary sheave (3 b) and a movablesheave (3 a) and which is disposed in a drive wheel; and a powertransmission chain (1) with an endless shape which is wound around thepulleys. At this time, a hydraulic actuator allows the movable sheaves(2 b) and (3 a) to move close or away to or from the stationary sheaves(2 a) and (3 b) so as to clamp the chain (1) by hydraulic pressure. Bymeans of the clamp force, a contact load occurs between the pulleys (2)and (3) and the chain (1) so as to transmit a torque by a friction forceof the contact portion.

Also, JP-A-2004-251385 discloses a power transmission chain including aplurality of links having front and back insertion through holes throughwhich pins are inserted; and a plurality of first and second pins whichconnect links, which are arranged in the chain width direction so as toallow the front insertion through hole of one link to correspond to theback insertion through hole of the other link, so as to be bendable inthe longitudinal direction. In JP-A-2004-251385, the pin is manufacturedsuch that a predetermined bar-like intermediate material is formed by aforging work, a turning work, a cutting work, and then a grinding workis performed on the bar-like intermediate material so as to allow a pinsection to have a predetermined shape.

In the power transmission chain in JP-A-2004-251385, a plurality of pinsare used, but it takes much time for working a pin, since an end portionof the pin needs to be subjected to a grinding work, which induces anincrease in manufacture cost.

SUMMARY OF THE INVENTION

An object of the invention is to provide a power transmission chain pincapable of reducing a manufacture cost by reducing a pin work time, anda manufacture method thereof.

According to an aspect of the invention, there is provided a powertransmission chain pin which is press-fitted to links arranged in achain width direction of a power transmission chain, the powertransmission chain pin comprising:

a guide portion disposed in at least one end portion of the powertransmission chain pin and inclined so as to gradually increase apress-fitting margin to facilitate a press-fitting operation,

wherein the guide portion is formed by a cold forging work.

In the power transmission chain according to the invention, in general,two types of pins (first and second pins) with a different sectionalshape are used, and at least one of the first and second pins comes intocontact with the pulley so as to transmit a power by the friction force.In the chain in which one of pins comes into contact with the pulley,one of the first and second pins corresponds to a pin (hereinafter,referred to as “first pin” or “pin”) which comes into contact with thepulley at the time the chain is used in a continuously variabletransmission, and the other thereof corresponds to a pin (which iscalled “interpiece” or “strip”, and hereinafter, referred to as “secondpin” or “interpiece”) which does not come into contact with the pulley.The section of the first pin needs to be formed in a predeterminedcurvature shape (double rounded shape, sphere, etc.), but the section ofthe second pin needs not to be formed in a predetermined curvatureshape. However, it is desirable to form a guide portion in the endportion thereof in that all of the first and second pins arepress-fitted to the links. At this time, the guide portion is formed bya cold forging work.

As a material of the pin, appropriate steel such as bearing steel isused.

In a known power transmission chain, a front end portion upper edge ofthe pin is first press-fitted to a through-hole of the link, and a frontend portion lower edge thereof is press-fitted to a through-hole thereoflater on. On the contrary, in the power transmission chain pin accordingto the invention, for example, the end portion of the pin is providedwith the guide portion for allowing the upper and lower edges of the pinto be press-fitted thereto at the same time. The guide portion may beprovided on an end portion which corresponds to a front end side at thetime of carrying out the press-fitting operation, and may be provided onboth end portions if necessary.

In general, the pin having such a guide portion is manufactured asfollows:

A drawing work is performed on a wire rod so as to have a requiredsectional shape. Subsequently, a pressing work is performed thereon soas to obtain an end surface with an inclined shape. Subsequently, a heattreatment work is further performed thereon. Subsequently, a grinding(or polishing) work is performed thereon by a grinding stone. However,the guide portion of the power transmission chain pin according to theinvention is formed by a cold forging work.

According to another aspect of the invention, there is provided a methodof manufacturing a power transmission chain pin which connects linksarranged in a chain width direction of a power transmission chain, themethod comprising:

a rough sectional shape formation step of drawing a wire rod so that asection thereof is formed in a substantially oval shape; and

a rough end portion shape formation step of cutting a continuousbar-like member which has been subjected to the drawing work into apredetermined length so that an end surface thereof has a predeterminedangle with respect to an axial direction;

wherein a final sectional shape and a final end portion shape of thepower transmission chain pin are formed by a cold forging work to thebar-like member cut into the predetermined length, which is a finalshape formation step.

The above-described method does not include a grinding step of grindingan end portion of the bar-like member of a predetermined length by agrinding stone.

Since the sectional shape obtained in the rough sectional shapeformation step needs not to be a final shape, the sectional shape isdetermined in consideration of facilitation for a drawing work and atreatment work in the subsequent step. Accordingly, the sectional shapemay be formed in an oval shape or a shape in which a part of an oval isa straight line. The predetermined angle with respect to the axialdirection in the rough end portion shape formation step is set to aninclination angle corresponding to the inclined surface of the pulley incase of the first pin which comes into contact with the pulley. Thepredetermined angle is not particularly limited in case of the secondpin which does not come into contact with the pulley, but may be set toan angle perpendicular to the axial direction or an inclination anglecorresponding to the inclined surface of the pulley. In general, thefinal shape formation step includes a plurality of steps (using aplurality of molding dies). In this case, the final sectional shape maybe first formed or the final end portion shape may be first formed.

“The grinding step of performing a grinding work by a grinding stone”includes all cutting works using a grinding stone, regardless of anobtained surface roughness. In the method of manufacturing the powertransmission chain pin according to the invention, a barrel work or aheat treatment work which are surface finishing works other than thecutting works may be carried out if necessary.

According to the method of manufacturing the power transmission chainpin according to the invention, it is possible to manufacture the powertransmission chain pin without the grinding step of grinding the endportion of the bar-like member, which has been cut into a predeterminedlength, using a grinding stone. Since the method does not include thegrinding step, a work time is reduced. Additionally, it is not necessaryto use a grinding fluid of which a waste fluid deteriorates anenvironment.

The power transmission chain pin according to the invention and the pinwhich is manufactured by the method of manufacturing the powertransmission chain pin according to the invention may be appropriatelyapplicable to a power transmission chain including a plurality of linkshaving front and back insertion through holes through which the pin isinserted; and a plurality of first and second pins which are arranged infront and back thereof and which connect the links arranged in the chainwidth direction so that the front insertion through hole of one linkcorresponds to the back insertion through hole of the other link. Atthis time, the first and second pins move while coming into rollingcontact with each other, so that the links are bendable in thelongitudinal direction. One of the first and second pins is press-fittedto the front insertion through hole of one link to be fixed and isfitted to the back insertion through hole of the other link so as to bemovable. The other pin is fitted to the front insertion through hole ofone link so as to be movable and is press-fitted to the back insertionthrough hole of the other link so as to be fixed thereto.

In this case, an example of a material of the link includes a springsteel or a carbon tool steel. An example of a material of the link isnot limited to the spring steel or the carbon tool steel, but may be, ofcourse, other steel such as a bearing steel. For example, the link ismanufactured such that a steel sheet is subjected to a press punchingwork, a barrel work, and a heat treatment work, and a shot work.

It is desirable that the press-fitting operation of the pin is carriedout at the edge (upper and lower edges) of a portion perpendicular tothe longitudinal direction of the insertion through hole. For example,the power transmission chain is manufactured such that necessary pinsare vertically held on a table and then one sheet of link or multiplesheets of links are press-fitted thereto.

The power transmission chain to which the pin according to the inventionis applied may be appropriately used in a power transmission apparatusincluding a first pulley which has a sheave surface with a conicalshape; a second pulley which has a sheave surface with a conical shape;and a power transmission chain which is wound around the first andsecond pulleys. Such a power transmission apparatus may be appropriatelyused as a continuously variable transmission of an automobile etc.

Further, in a power transmission chain comprising:

a plurality of links each of which has a front insertion through holeand a back insertion through hole through which pins are inserted; and

first pins and second pins connecting bendably the links in a chainlongitudinal direction such that the front insertion through hole of onelink corresponds to the back insertion through hole of another linkwhich is arranged to overlap with said one link in a chain widthdirection,

at least one of the first pins and second pins may be the powertransmission chain pin as described above.

The above described method of manufacturing a power transmission chainpin may be carried out in such a state that a lower die used in the coldforging for forming the final end portion shape of the powertransmission chain pin includes a concave portion for forming a guideportion of the power transmission chain pin, and an upper die includes aconcave portion for forming a surface of the power transmission chainpin coming into contact with a conical sheave surface of a pulley, and

the final end portion shape of the pin is formed by hitting a surface ofthe power transmission chain pin opposite to the guide portion by apunch.

According to the power transmission chain pin and the manufacture methodthereof, since a cold forging work is carried out, it is not necessaryto carry out a cut step. Accordingly, it is possible to reduce a pinwork time, and thus it is possible to reduce a manufacture cost.Moreover, it is possible to prevent a deterioration of an environmentdue to a grinding waste fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view illustrating a part of a power transmission chainto which a power transmission chain pin according to the invention isapplied.

FIG. 2 is an enlarged side view of a link.

FIG. 3 is a view schematically illustrating a state where the powertransmission chain according to the invention is press-fitted to a link.

FIG. 4 is a view schematically illustrating a shape of the powertransmission chain pin according to another embodiment of the invention.

FIG. 5 is a view schematically illustrating a drawing work step which isa first step of a manufacture method of the power transmission chain pinaccording to the invention.

FIG. 6 is a view schematically illustrating a cut step which is a secondstep of the manufacture method of the power transmission chain pinaccording to the invention.

FIGS. 7A and 7B are views schematically illustrating a cold forging stepwhich is a third step of the manufacture method of the powertransmission chain pin according to the invention.

FIG. 8 is a front view illustrating a state where the power transmissionchain is attached to a pulley.

FIG. 9 is a perspective view illustrating a continuously variabletransmission.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an exemplary embodiment of the invention will be describedwith reference to the accompanying drawings. In the description asbelow, “upper and lower” indicates upper and lower sides in FIG. 2.

FIG. 1 illustrates a part of a power transmission chain to which a powertransmission chain pin according to the invention is applied. A powertransmission chain (1) includes a plurality of links (11) which have afront insertion through hole (12) and a back insertion through hole (13)arranged at a predetermined distance in a chain length direction, and aplurality of pins (first pin) (14) and interpieces (second pin) (15)which connect the links (11) arranged in the chain width direction so asto be bendable in the chain length direction. The interpiece (15) isshorter than the pin (14). The interpiece (15) is disposed in the frontside and the pin (14) is disposed in the back side so as to be opposedto the interpiece (15).

One link unit is configured by arranging three link rows having aplurality of links with a coordinate phase arranged in the widthdirection in the chain movement direction (front/back direction). Thechain (1) is configured by plurally connecting the link unit having thethree link rows in the chain movement direction. In the embodiment, twoof the link row having eight sheets of links and the link row havingnine sheets of links configure one link unit.

As shown in FIG. 2, a column portion (21) is interposed between thefront insertion through hole (12) and the back insertion through hole(13) of the link (11). The front insertion through hole (12) includes apin movable portion (16) to which the pin (14) is movably fitted and aninterpiece fixation portion (17) to which the interpiece (15) is fixed.The back insertion through hole (13) includes a pin fixation portion(18) to which the pin (14) is fixed and an interpiece fixation portion(19) to which the interpiece (15) is movably fitted.

The width of the pin (14) is larger than that of the interpiece (15) inthe front/back direction. In the upper and lower edges of the interpiece(15), protrusion edge portions (15 a) and (15 b) which extend toward thepin (14) are disposed.

In FIG. 2, positions denoted by Signs A and B are lines (point in asectional view) where the pin (14) and the interpiece (15) come intocontact with each other in the straight line portion of the chain (1). Adistance between A and B is a pitch.

At the time of connecting the links (11) arranged in the chain widthdirection, the links (11) overlap with each other so that the frontinsertion through hole (12) of one link (11) corresponds to the backinsertion through hole (13) of the other link (11). Subsequently, thepin (14) is fixed to the back insertion through hole (13) of one link(11) and is movably fitted to the back insertion through hole (12) ofthe other link (11). Subsequently, the interpiece (15) is movably fittedto the back insertion through hole (13) of one link (11) and is fixed tothe front insertion through hole (12) of the other link (11).Accordingly, the pin (14) and the interpiece (15) move while coming intorolling contact with each other, and thus the links (11) are bendable inthe length direction (front/back direction).

At the boundary portion between the pin fixation portion (18) of thelink (11) and the interpiece movable portion (19), there is providedupper and lower hold portions (18 a) and (18 b) with a convex arc shapewhich are connected to upper and lower guide portions (19 a) and (19 b)with a concave arc shape of the interpiece movable portion (19) andwhich hold the pin (14) fixed to the pin fixation portion (18). In thesame manner, at the boundary portion between the interpiece fixationportion (17) and the pin movable portion (16), there is provided upperand lower hold portions (17 a) and (17 b) with a convex arc shape whichare connected to upper and lower guide portions (16 a) and (16 b) with aconcave arc shape of the pin movable portion (16) and which hold theinterpiece (15) fixed to the interpiece fixation portion (17).

A trace of a contact position between the pin (14) and the interpiece(15) on the basis of the pin (14) is formed in an involute curve. In theembodiment, a contact surface of the pin (14) is formed in an involuteshape in a sectional view so as to have a basic circle having a radiusRb and a center M, and a contact surface of the interpiece (15) isformed in a flat surface (straight line in a sectional view).Accordingly, when the link (11) moves from the straight line portion tothe curve portion of the chain (1) or moves from the curve portion tothe straight line portion, in the front insertion through hole (12), thepin (14) moves in the pin movable portion (16) while the contact surfacecomes into rolling contact (which includes a slight sliding contact)with the contact surface of the interpiece (15) with respect to theinterpiece (15) which is in the fixed state. In the back insertionthrough hole (13), the interpiece (15) moves in the interpiece movableportion (19) while the contact surface comes into rolling contact (whichincludes a slight sliding contact) with the contact surface of the pin(14) with respect to the pin (14) which is in the fixed state.

In the power transmission chain (1), since the pin moves repeatedly inthe vertical direction, a polygonal vibration occurs, which causes anoise. However, since the pin (14) and the interpiece (15) move whilecoming into rolling contact with each other and the trace of the contactposition between the pin (14) and the interpiece (15) on the basis ofthe pin (14) is formed in an involute curve shape, it is possible toreduce the vibration compared with a case where the contact surfaces ofthe pin and the interpiece are formed in an arc shape. Accordingly, itis possible to reduce the noise.

The power transmission chain (1) is used in a pulley type CVT shown inFIG. 8. However, at this time, the end surface of the pin (14) comesinto contact with sheave surfaces (2 c) and (2 d) with conical shapes ofthe pulley (2) in the state where the end surface of the interpiece (15)does not come into contact with the sheave surfaces (2 c) and (2 d) withthe conical shapes of a stationary sheave (2 a) and a movable sheave (2b) of the pulley (2) having a pulley shaft (2 e), and then a power istransmitted by a friction force generated by the contact. As describedabove, since the pin (14) and the interpiece (15) move while coming intorolling contact with each other, the pin (14) hardly rotates withrespect to the sheave surfaces (2 c) and (2 d) of the pulley (2), andthus a friction loss is reduced. Accordingly, it is possible to ensurean excellent power transmission rate.

In FIG. 8, when the movable sheave (2 b) of the drive pulley (2) is madeto move close or away to or from the stationary sheave (2 a), a wounddiameter of the chain (1) is large at the time of moving close theretoand is small at the time of moving away therefrom. In a driven pulley(3), although it is not shown in the drawing, when the movable sheavemoves in a direction opposite to the movable sheave (2 b) of the drivepulley (2) and the wound diameter of the drive pulley (2) becomes large,the wound diameter of the driven pulley (3) becomes small.Alternatively, when the wound diameter of the drive pulley (2) becomessmall, the wound diameter of the driven pulley (3) becomes large. As aresult, on the basis of the state where the transmission ratio is one toone (initial value), it is possible to obtain an U/D (under drive) statewhere the wound diameter of the drive pulley (2) is minimum and thewound diameter of the driven pulley (3) is maximum. Additionally, it ispossible to obtain an O/D (over drive) state where the wound diameter ofthe drive pulley (2) is maximum and the wound diameter of the drivenpulley (3) is minimum.

As shown in FIG. 8, the pin (14) includes a link hold portion (31) ofwhich a sectional shape is uniform and to which the link (11) ispress-fitted, and pulley contact portions (32) and (33) which are formedin both ends of the link hold portion (31) and which has inclinedsurfaces (32 a) and (33 a) corresponding to the sheave surfaces (2 c)and (2 d) of the pulley (2). At this time, the upper and lower edgeportions of the pin (14) are press-fitted to the upper and lower edgeportions of the through-portion (12) of the link (11), and then the pin(14) and the link (11) are coupled to each other. The interpiece (15)does not come into contact with the pulley and the upper and lower edgeportions of the interpiece (15) are press-fitted to the upper and loweredge portions of the through-hole (12) of the link (11). Accordingly,the interpiece (15) and the link (11) are coupled to each other.

The power transmission chain (1) is manufactured such that the necessarypins (14) and interpieces (15) are held on a table in a vertical shapeand then one sheet or multiple sheets of the links (11) are press-fittedthereto. The press-fitting margin is set in the range of 0.005 mm to 0.1mm. Then, pretension is loaded on the assembled chain (1).

FIG. 3 illustrates a state where the link (11) is press-fitted to thepin (14) according to the invention. In the end portion of the pin (14)which corresponds to the front end side at the time of carrying out thepress-fitting operation, there is provided a guide portion (34) foreasily carrying out the press-fitting operation. That is, in the endportion of each pin (14), there are provided inclined surfaces (32 a)and (33 a) corresponding to the shape of the sheave with which the endsurface comes into contact. At this time, there are provided a front endportion upper edge (14 a) which is first fitted to the through-hole (12)of the link (11) at the time of carrying out the press-fitting operationand a front end portion lower edge (14 b) which is finally fitted to thethrough-hole (12) of the link (11) at the time of carrying out thepress-fitting operation. The front end portion upper edge (14 a) isformed in an inclined shape so as to configure the guide portion (34).Accordingly, the press-fitting margin of the front end portion edge (14a) which is located more in the front end side than the front endportion lower edge (14 b) is set to 0. Therefore, a stress concentrationat the time of carrying out the press-fitting operation is reduced, andthus a deformation and a cut of the link (11) is prevented, so that astrength reduction of the link (11) is prevented. Additionally, ageneration amount of an abrasion powder is reduced, and a frictionbetween the links (11) is reduced. Accordingly, it is possible to reducea bending torque of the chain (1).

In the pin (14) shown in FIG. 3, only the front end portion upper edge(14 a) is formed in an inclined shape to configure the guide portion(34), compared with a known example. However, the shape of the guideportion is not limited thereto, but may be modified into various shapesso long as the upper and lower edge portions of the pin (14) arepress-fitted at the same time. For example, the front end portion upperedge of the pin (14) is eliminated, and also the front end portion loweredge may be eliminated at the same time. The example is shown in FIG. 4.In FIG. 4, at the boundary portion between the upper edge portion of apulley contact portion (32), which corresponds to the front end side atthe time of carrying out the press-fitting operation, and the upper edgeof a link hold portion (31), there is provided an inclined surface (35a) of which the press-fitting margin gradually increases. Also, at theboundary portion between the lower edge portion of the pulley contactportion (32) which corresponds to the front end side at the time ofcarrying out the press-fitting operation and the lower edge of the linkhold portion (31), there is provided an inclined surface (35 b) of whichthe press-fitting margin gradually increases. As a result, a guideportion (35) for carrying out the easy press-fitting operation isformed. Accordingly, a force acting on the inclined surface (35 a) ofthe upper edge and a force acting on the inclined surface (35 b) of thelower edge are substantially equal to each other. The press-fittingoperation is easier and a stress concentration at the time of carryingout the press-fitting operation is reduced.

FIGS. 5 to 7B illustrate a manufacture method of the power transmissionchain pin according to the invention that is suitable for manufacturingthe pin (14) having the guide portions (34) and (35). The manufacturemethod includes a rough sectional shape formation step (see FIG. 5) ofdrawing a wire rod (which is the same as the known example) so that thesection thereof is formed in a substantially oval shape; a rough endportion shape formation step (see FIG. 6) of cutting a continuousbar-like member (W1) which has been subjected to the drawing work into apredetermined length, so that the end surface thereof has apredetermined angle with respect to the axial direction; and a finalshape formation step (see FIGS. 7A and 7B) of cold forging a bar-likemember (W2) which has been cut into a predetermined length, so as tohave a final sectional shape and a final end portion shape.

In FIG. 5, a drawing work die (51) includes a die hole of which asection is formed in an oval (or ellipsoidal) shape. In the drawingwork, a bearing steel wire becomes the bar-like member (W1) with acontinuous shape and an oval (or ellipsoidal) shape in a sectional view.It is not necessary to particularly manage precision or scar so long asthe section is a rough shape. Accordingly, it is possible to remarkablyreduce a work cost, compared with a drawing work in which a particularmanagement is necessary to obtain a final shape.

In FIG. 6, a cut surface of the bar-like member (W1) with a continuousshape is not formed at a right angle with respect to the axial directionof the bar-like member (W1), but is formed so that both ends are formedat a predetermined angle by first and second cutters (62) and (63).Additionally, in FIG. 6, the upper and lower portions of the bar-likemember (W2) of a predetermined length are cut out so as to be disposedon the same side at a normal time. However, in order to obtain thebar-like member (W2) of a predetermined length, the bar-like member (W2)may be cut out so that the upper and lower portions thereof arealternatively disposed.

The final shape formation step includes a cold forging step (see FIG.7A) of a final sectional shape formation for obtaining a final sectionalshape by a cold forging work, and a cold forging step (see FIG. 7B) of afinal end portion formation for obtaining a final end portion shape by acold forging work. As shown in FIGS. 7A and 7B, a cold forging device(71) includes holders (72) and (76), lower dies (73) and (77) and upperdies (74) and (78) which are held by the holders (72) and (76), andpunches (75) and (79) which can move in the vertical direction. In thelower die (73) used in the cold forging step of the final sectionalshape formation, there is provided a concave portion for forming arolling contact surface of the pin (14). In the upper die (74), there isprovided a concave portion for forming upper and lower press-fittingportions of the pin (14). Accordingly, the punch (75) is worked so as tohit a surface opposite to the rolling contact surface. Consequently, thefinal sectional shape of the pin (14) is formed. Additionally, in alower die (77) used in the cold forging step of the final end portionformation, there is provided a concave portion for forming the guideportion (34) for carrying out an easy press-fitting operation. In anupper die (78), there is provided a concave portion for forming surfaces(32 a) and (33 a) coming into contact with the sheave surfaces (2 c) and(2 d) with a conical shape of the pulleys (2) and (3). Accordingly, thepunch (79) is worked so as to hit a surface opposite to the guideportion (34). Consequently, the final end portion shape of the pin (14)is formed. In this way, a grinding (which includes a polishing) workwhich was necessary for a known end surface treatment work using a grindstone is not necessary. Further, it is possible to obtain a final shapeof the pin (14) without a grinding work which is necessary to form theguide portion (34) for a press-fitting operation. Additionally, in FIGS.7A and 7B, the cold forging step is divided into two steps for adescription, but is not limited to the two steps.

Of course, the manufacture method of the pin is applicable to theinterpiece (15) in which a limitation of the end surface is less and aguide portion is desirably disposed. Further, the manufacture method isapplicable to a pin that is used in a chain in which the first andsecond pins having the same lengths as each other come into contact withsheave surfaces or a pin that is used in other various type powertransmission chains.

1. A power transmission chain pin which is press-fitted to linksarranged in a chain width direction of a power transmission chain, thepower transmission chain pin comprising: a guide portion disposed in atleast one end portion of the power transmission chain pin and inclinedso as to gradually increase a press-fitting margin to facilitate apress-fitting operation, wherein the guide portion is formed by a coldforging work.
 2. A power transmission chain comprising: a plurality oflinks each of which has a front insertion through hole and a backinsertion through hole through which pins are inserted; and a pluralityof first pins and a plurality of second pins connecting bendably thelinks in a chain longitudinal direction such that the front insertionthrough hole of one link corresponds to the back insertion through holeof another link which is arranged to overlap with said one link in achain width direction, wherein at least one of said first pins andsecond pins is the power transmission chain pin according to claim
 1. 3.A method of manufacturing a power transmission chain pin which connectslinks arranged in a chain width direction of a power transmission chain,the method comprising: a rough sectional shape formation step of drawinga wire rod so that a section thereof is formed in a substantially ovalshape; and a rough end portion shape formation step of cutting acontinuous bar-like member which has been subjected to the drawing workinto a predetermined length so that an end surface thereof has apredetermined angle with respect to an axial direction; wherein a finalsectional shape and a final end portion shape of the power transmissionchain pin are formed by a cold forging work to the bar-like member cutinto the predetermined length, which is a final shape formation step. 4.A method of manufacturing a power transmission chain pin, according toclaim 3, wherein a lower die used in the cold forging for forming thefinal end portion shape of the power transmission chain pin includes aconcave portion for forming a guide portion of the power transmissionchain pin, and an upper die includes a concave portion for forming asurface of the power transmission chain pin coming into contact with aconical sheave surface of a pulley, and the final end portion shape ofthe pin is formed by hitting a surface of the power transmission chainpin opposite to the guide portion by a punch.